This application claims priority to German Application No. 199 10 910.0, filed on Mar. 11, 1999.
The invention relates to a method of carrying out a fiber or paper manufacturing process using a plurality of successive method steps in which defined process steps are carried out by means of predefinable chemical and physical sequences and process optimization is performed on the basis of measured values and characteristic values formed from the latter, if appropriate by using state models.
In the manufacture and preparation of fibrous materials, and also in paper manufacture, it is usual for a plurality of process steps to be connected in series, in order at the end of the overall process to obtain the respective product in a desired quality.
An important method step in the manufacture of paper is represented by the bleaching of fibrous materials. The respective stock, which may be, for example, groundwood, refiner stock and/or waste-paper stock, is subjected to bleaching operations in order to achieve the desired increase in the brightness of the stock without, in the process, impairing the strength of the respective stock in an undesired way. Since in the preparation of fibrous material or paper manufacture, significant importance is placed on the bleaching apparatus, normally consisting of a plurality of stages, to achieve desired qualities, attempts are already being made in practice to optimize the bleaching process. It is also already known to use optimization methods of this type in cooking processes in conjunction with the manufacture of chemical pulps. In this connection, it is known in particular to use state models and/or process models, specifically those based on registered mechanical, physical and/or chemical properties of the fibrous material or of the fibrous material suspension. Subprocesses of an overall process, such as the bleaching stage, are optimized using such state or process models.
The object of the invention is to optimize overall processes in the manufacture and preparation of fibrous materials or in paper manufacture both from technological points of view and also from economic and ecological points of view.
On the basis of the method specified at the beginning, according to the invention this is achieved by at least those characteristic variables of all the individual method steps which influence the target variables of the respective end product of the method in a significant way being registered on line and being used directly or indirectly on line to control or optimize the overall process, characteristic variables being formed both on the basis of the starting materials or raw materials and of the chemicals, auxiliaries and energy supplied in the successive method steps as well as of the materials and emissions to be disposed of.
In addition to the on line registration of characteristic variables, according to one design variant of the invention, off-line determination can also be performed so that, using the discrete values obtained here, on-line values are optimized within the context of an autocalibration module by means of computational models.
A significant special feature of the method according to the invention can also be seen in the fact that not only the determination of characteristic variables but also the monitoring and the control or optimization is carried out on line, to be specific preferably on the basis of known mathematical or economic algorithms, on the basis of fuzzy logic and the like.
A further significant aspect of the invention is that at least some, and preferably all, of the target and characteristic variables are transformed by means of a computational unit on a unitary basis. It is possible for a unitary basis to be a price per unit quantity determined via the determination of a cost or value. As a result of the conversion to a unitary basis, it is then also possible for a so-called bottleneck optimization to be carried out. From an economic point of view, the bottleneck problem is part of the production planning process. In this case, the products are designed via their price and quantity. On this basis, a mathematical target function is then defined and, as a rule, is designed as a profit or production maximization. However, it is also conceivable to define a function which, for example, has the objective of a reduced quantity of residual materials (waste) (f(x1+. . . +xn)xe2x88x92 greater than MIN). These functions may be linear, but do not necessarily have to be. This actual target function, which can therefore be a maximization function, a minimization function or a combination of the two, can be restricted by ancillary conditions. The ancillary conditions can be formulated, for example, as a sales condition (for example upper sales limit) or a capacity condition (for example capacity bottleneck), which further restrict the target function. In addition, in the sense of the invention it is the case that both the target function and also the ancillary conditions are not formulated rigidly but are adapted to the respective conditions and requirements which result from the continuous operation (cf. Hax, H.: Lineare Planungsrechnung und Simplex-Methode als Instrument betrieblicher Planung [Linear planning calculation and simplex methods as an instrument of operational planning], in: ZfhF 1960, pp. 576 ff.).
Further advantageous embodiments and features of the invention are specified in the subclaims and will be explained below using an illustration of the principle.